/Engine/Source/Editor/UnrealEd/Public/SnappingUtils.h
Snaps actors to the nearest vertex on another actor
true if anything was snapped
static bool SnapDraggedActorsToNearestVertex ( FVector & DragDelta, [FLevelEditorViewportClient](API\Editor\UnrealEd\FLevelEditorViewportClient) * ViewportClient )